Imaging lens

ABSTRACT

An imaging lens includes a first lens group that includes sequentially from an object side, a first lens formed of resin and having a positive refractive power and a second lens formed of resin and having a negative refractive power, the first lens and the second lens collectively forming a cemented lens having a positive refractive power. The imaging lens further includes a second lens group that includes a negative lens having a convex surface directed toward an image plane and a third lens group that includes a positive lens, where the first lens group, the second lens group, and the third lens groups are sequentially arranged from the object side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging lens, suitable for an imaging device equipped with solid imaging elements.

2. Description of the Related Art

In recent years, the prevalence of portable electronic imaging devices, such as cellular phones, digital cameras and the like, has been spreading widely. Recent reductions in the size of electronic imaging devices has lead to demand for smaller imaging lenses equipped on electronic imaging devices. In response to such demand, numerous imaging lenses have been proposed, such as those disclosed in Japanese Patent Application Laid-Open Publication Nos. 2006-163340; 2006-284620; 2002-228922; and 2006-98976.

The imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2006-163340 includes three lenses arranged in three groups and employs only lenses made of a plastic material. The imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2006-284620 is a wide angle lens realizing fine chromatic aberration correction by cementing lenses made of a plastic material. The imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2002-228922 is a lens realizing fine chromatic aberration correction by cementing lenses made of a glass material. Further, the imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2006-98976 is a lens that incorporates a low dispersion glass in a first lens group to realize fine chromatic aberration correction.

Recent demand for higher image quality has accelerated advances in high pixel formation of imaging elements. In general, high pixel formation of an imaging element is achieved by minimizing the cell size thereof or by enlarging the imaging element. However, in the former case, light intensity deteriorates, and in the latter case, chromatic aberration can not be easily corrected because the focal length of the imaging lens has to be lengthened.

Although a lens formed of a low dispersion glass material, such as the lens as disclosed in Japanese Patent Application Laid-Open Publication No. 2006-98976, may overcome such problems, the production cost of the imaging lens increases since the low dispersion glass material is expensive. Also, there is a problem of increased weight resulting from the use of glass material. With respect to the imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2002-228922, although use of a low dispersion glass material in a cemented lens enables correction of chromatic aberration, problems similar to those associated with the imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2006-98976 arise.

Meanwhile, with the imaging lenses respectively disclosed in Japanese Patent Application Laid-Open Publication Nos. 2006-163340 and 2006-284620, the range of choice concerning refractive index/dispersion ratio is narrow for resin materials, making correction of chromatic aberration caused by high pixel formation of the imaging element difficult.

In order to overcome the problems of above mentioned prior arts, an object of the present invention is to provide a small, low-cost, and light-weight imaging lens having high optical performance satisfying high pixel formation of imaging element, even when inclusive of a lens formed of resin.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least solve the above problems in the conventional technologies.

An imaging lens according to one aspect of the present invention includes a first lens group that includes sequentially from an object side, a first lens formed of resin and having a positive refractive power and a second lens formed of resin and having a negative refractive power, the first lens and the second lens collectively forming a cemented lens having a positive refractive power. The imaging lens further includes a second lens group that includes a negative lens having a convex surface directed toward an image plane and a third lens group that includes a positive lens, where the first lens group, the second lens group, and the third lens groups are sequentially arranged from the object side.

The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view along the optical axis of an imaging lens according to a first embodiment;

FIG. 2 is a spherical aberration diagram of the image lens according to the first embodiment;

FIG. 3 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the first embodiment;

FIG. 4 is a cross-sectional view along the optical axis of an imaging lens according to a second embodiment;

FIG. 5 is a spherical aberration diagram of the image lens according to the second embodiment;

FIG. 6 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the second embodiment;

FIG. 7 is a cross-sectional view along the optical axis of an imaging lens according to a third embodiment;

FIG. 8 is a spherical aberration diagram of the image lens according to the third embodiment;

FIG. 9 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the third embodiment;

FIG. 10 is a cross-sectional view along the optical axis of an imaging lens according to a fourth embodiment;

FIG. 11 is a spherical aberration diagram of the image lens according to the fourth embodiment;

FIG. 12 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the fourth embodiment;

FIG. 13 is a cross-sectional view along the optical axis of an imaging lens according to a fifth embodiment;

FIG. 14 is a spherical aberration diagram of the image lens according to the fifth embodiment;

FIG. 15 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the fifth embodiment;

FIG. 16 is a cross-sectional view along the optical axis of an imaging lens according to a sixth embodiment;

FIG. 17 is a spherical aberration diagram of the image lens according to the sixth embodiment;

FIG. 18 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the sixth embodiment;

FIG. 19 is a cross-sectional view along the optical axis of an imaging lens according to a seventh embodiment;

FIG. 20 is a spherical aberration diagram of the image lens according to the seventh embodiment;

FIG. 21 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the seventh embodiment;

FIG. 22 is a cross-sectional view along the optical axis of an imaging lens according to an eighth embodiment;

FIG. 23 is a spherical aberration diagram of the image lens according to the eighth embodiment;

FIG. 24 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the eighth embodiment;

FIG. 25 is a cross-sectional view along the optical axis of an imaging lens according to a ninth embodiment;

FIG. 26 is a spherical aberration diagram of the image lens according to the ninth embodiment;

FIG. 27 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the ninth embodiment;

FIG. 28 is a cross-sectional view along the optical axis of an imaging lens according to a tenth embodiment;

FIG. 29 is a spherical aberration diagram of the image lens according to the tenth embodiment;

FIG. 30 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the tenth embodiment;

FIG. 31 is a cross-sectional view along the optical axis of an imaging lens according to an eleventh embodiment;

FIG. 32 is a spherical aberration diagram of the image lens according to the eleventh embodiment; and

FIG. 33 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the eleventh embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the accompanying drawings, exemplary embodiments according to the present invention are explained in detail below.

An imaging lens according to embodiments of the present invention includes sequentially from an object side, a first lens group, a second lens group and a third lens group. The first lens group includes sequentially from the object side, a first lens formed of resin and having a positive refractive power, and second lens formed of resin and having a negative refractive power, the first lens and the second lens collectively forming a cemented lens having a positive refractive power. The second lens group includes a negative lens. The third lens group includes a positive lens. Further, the imaging lens includes a diaphragm aperture of a given caliber provided close to an object-side surface of the first lens group or between the first lens group and the second lens group.

The imaging lens according to the present embodiments is a small, low-cost, and light-weight imaging lens having high optical performance that satisfies high pixel formation of an imaging element, even when inclusive of a lens formed of resin.

The imaging lens according to the present embodiments may be applied to an electronic imaging apparatus having an imaging element. An object of the present invention is to provide an imaging lens of a smaller size and higher optical performance in response to recent advancements in high pixel formation of imaging elements and reductions in device size. To this means, the following conditions are provided in addition to the arrangement described.

For the imaging lens according to the present embodiments, it is preferable to satisfy the following conditional expression, where f₁ is the focal length of the first lens group, and f is the focal length of the imaging lens.

0.5<f ₁ /f<1.0   (1)

Conditional expression (1) provides the ratio of focal length of the imaging lens and the focal length of the first lens group. By satisfying conditional expression (1), aberration can be effectively corrected. Beyond the lower limit of conditional expression (1), image distortion increases or spherical aberration and coma aberration becomes obvious. On the other hand, exceeding the upper limit of conditional expression (1) is not preferable because large chromatic aberration occurs.

Further, for the imaging lens according to the present embodiments, it is preferable to satisfy the following conditional expression, where the focal length of the first lens of the first lens group is f₁₁, and the focal length of the second lens of the first lens group is f₁₂.

0.3<|f ₁₁ /f ₁₂|<1.0   (2)

Conditional expression (2) provides the absolute value of the ratio of focal length of the second lens of the first lens group to the focal length of the first lens of the first lens group. By satisfying conditional expression (2), increase and decrease of the spherical aberration can be controlled. If the value of |f₁₁/f₁₂| is outside the range specified by conditional expression (2), spherical aberration cannot be sufficiently corrected.

Further, for the imaging lens according to the present embodiments, it is preferable to satisfy the following conditional expression, where the refractive index in d-line of the first lens of the first lens group is n₁, and the refractive index of d-line of the second lens of the first lens group is n₂.

0<n ₂ −n ₁   (3)

Conditional expression (3) provides the difference between the refractive index in d-line of the second lens of the first lens group, and the refractive index of d-line of the first lens of the first lens group. By satisfying conditional expression (3), aberration can be effectively corrected. For values below the lower limit of conditional expression (3), aberration correction becomes difficult and such values are not desirable.

Further, for the imaging lens according to the present embodiments, it is preferable to satisfy the following conditional expression, where OP is an overall length of the imaging lens (the distance from an object-side surface of the imaging lens nearest an object to the image plane), and 2Y is the diameter of effective image circle of the imaging lens.

OP/2Y<2.0   (4)

Conditional expression (4) provides the ratio of diameter of effective image circle and the overall length of the imaging lens. Satisfaction of conditional expression (4) enables provision of a smaller imaging lens having a shorter overall length. Exceeding the upper limit of conditional expression (4) is not preferable as the overall length of the imaging lens becomes too long.

The imaging lens according to the present embodiments will have higher optical performance and be smaller in size by satisfying conditional expressions (1) to (4) sequentially. It is preferable; however, to satisfy conditional expressions (2) and (3) at the same time.

Further, the imaging lens according to the present embodiments preferably includes at least one aspherical surface. Thereby, various aberrations can be corrected more effectively by fewer lenses, while achieving reductions in the size and weight of the optical system as well as in production costs. Further, forming the second lens group and/or the third lens group of resin enables provision of an imaging lens that is lower in cost and lighter.

The imaging lens according to the present invention has the characteristics explained above and enables provision of a small, low-cost, and light-weight imaging lens having high optical performance satisfying the high pixel formation of an imaging element, even when inclusive of a lens formed of resin. Further, the imaging lens includes an aspherical lens, thus, various aberrations can be corrected more effectively by fewer lenses, while achieving reductions in the size and weight of the optical system and in production costs.

FIG. 1 is a cross-sectional view along the optical axis of an imaging lens according to a first embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₁₁, a second lens group G₁₂, and a third lens group G₁₃. Further, an aperture ST of a given diameter is provided close to an object-side surface of the first lens group G₁₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₁₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) is arranged on the image plane IMG.

The first lens group G₁₁ includes sequentially from the object side, a first lens L₁₁₁ formed of resin and having a positive refractive power and a second lens L₁₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₁₂ includes a negative meniscus lens L₁₂₁, whose convex surface is directed toward the image plane IMG. Further, the lens L₁₂₁ is preferably formed of resin.

The third lens group G₁₃ includes a positive meniscus lens L₁₃₁, whose convex surface is directed toward the object side. Further, the lens L₁₃₁ is preferably formed of resin.

The object-side surface of the first lens L₁₁₁, the image-plane-IMG-side surface of the second lens L₁₁₂, both surfaces of the lens L₁₂₁, and both surfaces of the lens L₁₃₁ are aspherical.

Values concerning the imaging lens according to first embodiment are given below.

-   The focal length of the imaging lens (f)=5.85 -   The F number=2.92 -   The diameter of the effective image circle of the imaging lens     (2Y)=7.40 -   The focal length of the first lens group G₁₁ (f₁)=4.856 -   The focal length of the first lens L₁₁₁ of the first lens group G₁₁     (f₁₁)=2.802 -   The focal length of the second lens L₁₁₂ of the first lens group G₁₁     (f₁₂)=−5.262 -   The refractive index of d-line of the first lens L₁₁₁ of the first     lens group G₁₁ (n₁)=1.525 -   The refractive index of d-line of the second lens L₁₁₂ of the first     lens group G₁₁ (n₂)=1.586 -   (Values concerning conditional expression 1)

f ₁ /f=0.832

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0532

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.061

-   (Values concerning conditional expression 4)

OP/2Y=0.87

-   r₁=∞ (diaphragm aperture) -   d₁=0 -   r₂=1.85380 (aspherical surface) -   d₂=0.871 nd₁=1.525 νd₁=56.2 -   r₃=−5.98934 -   d₃=0.41 nd₂=1.586 νd₂=29.9 -   r₄=6.45573 (aspherical surface) -   d₄=0.756 -   r₅=−2.08317 (aspherical surface) -   d₅=0.537 nd₃=1.586 νd₃=29.9 -   r₆=−3.44932 (aspherical surface) -   d₆=0.755 -   r₇=2.54213 (aspherical surface) -   d₇=1.117 nd₄=1.525 ν₄=56.2 -   r₈=2.50984 (aspherical surface) -   d₈=0.40 -   r₉=∞ -   d₉=0.30 nd₅=1.524 νd₅=54.5 -   r₁₀=∞ -   d₁₀=1.278 -   r₁₁=∞ (image plane)     Constant of the cone (K) and aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (second surface) -   K=−0.03512, -   A₃=0, A₄=55.707×10⁻³, -   A₅=0, A₆=−1.576×10⁻², -   A₇=0, A₈=4.023×10⁻², -   A₉=0, A₁₀=−3.229×10⁻², -   A₁₁=0, A₁₂=−1.978×10⁻², -   A₁₃=0, A₁₄=44.407×10⁻², -   A₁₅=0, A₁₆=−1.788×10⁻²     (fourth surface) -   K=−1.98846, -   A₃=0, A₄=6.143×10⁻³, -   A₅=0, A₆=−3.557×10⁻², -   A₇=0, A₈=7.126×10⁻², -   A₉=0, A₁₀=−6.162×10⁻², -   A₁₁=0, A₁₂=−2.354×10⁻², -   A₁₃=0, A₁₄=5.690×10⁻², -   A₁₅=0, A₁₆=−2.183×10⁻²     (fifth surface) -   K=0, -   A₃=0, A₄=−1.325×10⁻¹, -   A₅=0, A₆=7.923×10⁻², -   A₇=0, A₈=−7.465×10⁻², -   A₉=0, A₁₀=4.804×10⁻², -   A₁₁=0, A₁₂=−5.208×10⁻³, -   A₁₃=0, A₁₄=−1.306×10⁻², -   A₁₅=0, A₁₆=−3.092×10⁻³     (sixth surface) -   K=0, -   A₃=0, A₄=−1.557×10⁻¹, -   A₅=0, A₆=1.178×10⁻¹, -   A₇=0, A₈=−5.78×10⁻², -   A₉=0, A₁₀=1.948×10⁻², -   A₁₁=0, A₁₂=2.511×10⁻³, -   A₁₃=0, A₁₄=−2.547×10⁻³, -   A₁₅=0, A₁₆=3.969×10⁻⁴     (seventh surface) -   K=−1.21976, -   A₃=0, A₄=−1.407×10⁻¹, -   A₅=0, A₆=3.988×10⁻², -   A₇=0, A₈=−6.326×10⁻³, -   A₉=0, A₁₀=1.962×10⁻⁴, -   A₁₁=0, A₁₂=6.793×10⁻⁵, -   A₁₃=0, A₁₄=−3.047×10⁻⁵, -   A₁₅=0, A₁₆=−3.789×10⁻⁷     (eighth surface) -   K=−5.38629, -   A₃=0, A₄=−5.964×10⁻², -   A₅=0, A₆=1.300×10⁻², -   A₇=0, A₈=−1.973×10⁻³, -   A₉=0, A₁₀=1.070×10⁻⁴, -   A₁₁=0, A₁₂=1.155×10⁻⁵, -   A₁₃=0, A₁₄=−2.297×10⁻⁵, -   A₁₅=0, A₁₆=1.074×10⁻⁷

FIG. 2 is a spherical aberration diagram of the image lens according to the first embodiment. FIG. 3 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the first embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 4 is a cross-sectional view along the optical axis of an imaging lens according to a second embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₂₁, a second lens group G₂₂, and a third lens group G₂₃. Further, an aperture ST of a given diameter is provided near an object-side surface of the first lens group G₂₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₂₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₂₁ includes sequentially from the object side, a first lens L₂₁₁ formed of resin and having a positive refractive power and a second lens L₂₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₂₂ includes a negative meniscus lens L₂₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₂₂₁ is preferably formed of resin.

The third lens group G₂₃ includes a positive meniscus lens L₂₃₁, whose convex surface is directed toward the object side. Further, the lens L₂₃₁ is preferably formed of resin.

The object-side surface of the first lens L₂₁₁, the image-plane-IMG-side surface of the second lens L₂₁₂, both surfaces of the lens L₂₂₁, and both surfaces of the lens L₂₃₁ are aspherical.

Values concerning the imaging lens according to second embodiment are given below.

-   The focal length of the imaging lens (f)=4.78 -   The F number=2.80 -   The diameter of the effective image circle of the imaging lens     (2Y)=6.00 -   The focal length of the first lens group G₂₁ (f₁)=3.982 -   The focal length of the first lens L₂₁₁ of the first lens group G₂₁     (f₁₁)=2.707 -   The focal length of the second lens L₂₁₂ of the first lens group G₂₁     (f₁₂)=−6.277 -   The refractive index of d-line of the first lens L₂₁₁ of the first     lens group G₂₁ (n₁)=1.531 -   The refractive index of d-line of the second lens L₂₁₂ of the first     lens group G₂₁ (n₂)=1.586 -   (Values concerning conditional expression 1)

f ₁ /f=0.833

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.431

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.055

-   (Values concerning conditional expression 4)

OP/2Y=0.88

-   r₁=1.45129 (aspherical surface) -   d₁=0.700 nd₁=1.531 νd₁=56.0 -   r₂=−129.12716 -   d₂=0.40 nd₂=1.586 νd₂=29.9 -   r₃=3.78684 (aspherical surface) -   d₃=0.902 -   r₄=−1.65506 (aspherical surface) -   d₄=0.547 nd₃=1.586 νd₃=29.9 -   r₅=−3.10199 (aspherical surface) -   d₅=0.394 -   r₆=−2.36455 (aspherical surface) -   d₆=1.125 nd₄=1.525 νd₄=56.2 -   r₇=2.632 (aspherical surface) -   d₇=0.35 -   r₈=∞ -   d₈=0.30 nd₅=1.518 νd₅=59.0 -   r₉=∞ -   d₉=0.587 -   r₁₀=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=−3.08725, -   A₃=3.518×10⁻³, A₄=2.082×10⁻¹, -   A₅=−5.238×10⁻¹, A₆=1.418, -   A₇=−2.032, A₈=1.495, -   A₉=5.074×10⁻¹, A₁₀=6.746×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (third surface) -   K=15.11916, -   A₃=6.041×10⁻², A₄=−2.207×10⁻¹, -   A₅=−5.133×10⁻¹, A₆=−8.556×10⁻¹, -   A₇=8.741×10⁻¹, A₈=−4.108×10⁻¹, -   A₉=4.996×10⁻⁵, A₁₀=−6.062×10⁻⁴ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fourth surface) -   K=1.98247, -   A₃=1.429×10⁻², A₄=−3.072×10⁻¹, -   A₅=6.895×10⁻¹, A₆=6.342×10⁻¹, -   A₇=4.543×10⁻², A₈=2.279×10⁻¹, -   A₉=−2.232×10⁻², A₁₀=−3.080×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=−0.76550, -   A₃=−1.370×10⁻¹, A₄=2.986×10⁻², -   A₅=−7.069×10⁻², A₆=1.170×10⁻¹, -   A₇=−5.009×10⁻², A₈=−3.744×10⁻², -   A₉=5.620×10⁻², A₁₀=−1.860×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=−0.75438, -   A₃=−1.072×10⁻¹, A₄==7.419×10⁻², -   A₅=5.708×10⁻², A₆=1.344×10⁻³, -   A₇=−3.754×10⁻³, A₈=−9.456×10⁻⁴, -   A₉=1.183×10⁻⁴, A₁₀=7.990×10⁻⁵ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−0.15401, -   A₃=−3.364×10⁻², A₄=−6.001×10⁻², -   A₅=2.268×10⁻², A₆=−2.223×10⁻³, -   A₇=−1.741×10⁻³, A₈=3.876×10⁻⁴, -   A₉=2.933×10⁻⁴, A₁₀=−1.170×10⁻⁴ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0

FIG. 5 is a spherical aberration diagram of the image lens according to the second embodiment. FIG. 6 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the second embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 7 is a cross-sectional view along the optical axis of an imaging lens according to a third embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₃₁, a second lens group G₃₂, and a third lens group G₃₃. Further, an aperture ST of a given diameter is provided near an object-side surface of the first lens group G₃₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₃₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₃₁ includes sequentially from the object side, a first lens L₃₁₁ formed of resin and having a positive refractive power and a second lens L₃₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₃₂ includes a negative meniscus lens L₃₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₃₂₁ is preferably formed of resin.

The third lens group G₃₃ includes a positive meniscus lens L₃₃₁ whose convex surface is directed toward the object side. Further, the lens L₃₃₁ is preferably formed of resin.

The object-side surface of the first lens L₃₁₁, the image-plane-IMG-side surface of the second lens L₃₁₂, both surfaces of the lens L₃₂₁, and both surfaces of the lens L₃₃₁ are aspherical.

Values concerning the imaging lens according to the third embodiment are given below.

-   The focal length of the imaging lens (f)=4.98 -   The F number=2.92 -   The diameter of the effective image circle of the imaging lens     (2Y)=6.00 -   The focal length of the first lens group G₃₁ (f₁)=4.344 -   The focal length of the first lens L₃₁₁ of the first lens group G₃₁     (f₁₁)=2.691 -   The focal length of the second lens L₃₁₂ of the first lens group G₃₁     (f₁₂)=−5.168 -   The refractive index of d-line of the first lens L₃₁₁ of the first     lens group G₃₁ (n₁)=1.531 -   The refractive index of d-line of the second lens L₃₁₂ of the first     lens group G₃₁ (n₂)=1.586 -   (Values concerning conditional expression 1)

f ₁ /f=0.872

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.521

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.055

-   (Values concerning conditional expression 4)

OP/2Y=0.95

-   r₁=1.58341 (aspherical surface) -   d₁=0.917 nd₁=1.531 νd₁=56.0 -   r₂=−11.76037 -   d₂=0.40 nd₂=1.586 νd₂=29.9 -   r₃=4.125 (aspherical surface) -   d₃=0.836 -   r₄=−2.47287 (aspherical surface) -   d₄=0.703 nd₃=1.613 νd₃=26.7 -   r₅=−2.78133 (aspherical surface) -   d₅=0.366 -   r₆=9.44476 (aspherical surface) -   d₆=1.490 nd₄=1.531 νd₄=56.0 -   r₇=3.41237 (aspherical surface) -   d₇=0.50 -   r₈=∞ -   d₈=0.30 nd₅=1.518 νd₅=59.0 -   r₉=∞ -   d₉=0.205 -   r₁₀=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     As, A₆, A₇, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=−4.15452, -   A₃=7.146×10⁻³, A₄=2.044×10⁻¹, -   A₅=−5.316×10⁻¹, A₆=1.420, -   A₇=−2.027, A₈=1.490, -   A₉=−5.031×10⁻¹, A₁₀=5.658×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (third surface) -   K=13.81959, -   A₃=4.732×10⁻², A₄=1.805×10⁻¹, -   A₅=5.334×10⁻¹, A₆=−8.526×10⁻¹, -   A₇=8.509×10⁻¹, A₈=−4.228×10⁻¹, -   A₉=2.232×10⁻², A₁₀=7.478×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fourth surface) -   K=−0.29440, -   A₃=−8.363×10⁻⁴, A₄=3.886×10⁻³, -   A₅=5.679×10⁻³, A₆=−2.671×10⁻³, -   A₇=−9.484×10⁻³, A₈=−8.873×10⁻³, -   A₉=−3.336×10⁻⁴, A₁₀=1.469×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=−7.55449, -   A₃=−2.262×10⁻², A₄=−1.388×10⁻³, -   A₅=2.063×10⁻⁰, A₆=2.306×10⁻³, -   A₇=1.829×10⁻³, A₈=1.122×10⁻³, -   A₉=8.136×10⁻⁴, A₁₀=−6.974×10⁻⁴ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=−89.52190, -   A₃=−2.169×10⁻², A₄=−9.918×10⁻³, -   A₅=1.090×10⁻³, A₆=1.902×10⁻³, -   A₇=7.176×10⁻⁴, A₈=3.015×10⁻⁵, -   A₉=1.254×10⁻⁴, A₁₀=−8.045×10⁻⁵ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−18.21906, -   A₃=1.801×10⁻², A₄=−2.269×10⁻², -   A₅=3.054×10⁻³, A₆=2.179×10⁻⁴, -   A₇=2.059×10⁻⁵, A₈=2.019×10⁻⁵, -   A₉=7.572×10⁻⁶, A₁₀=−1.810×10⁻⁵ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0

FIG. 8 is a spherical aberration diagram of the image lens according to the third embodiment. FIG. 9 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the third embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 10 is a cross-sectional view along the optical axis of an imaging lens according to a fourth embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₄₁, a second lens group G₄₂, and a third lens group G₄₃. Further, an aperture ST of a given diameter is provided near an object-side surface of the first lens group G₄₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₄₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₄₁ includes sequentially from the object side, a first lens L₄₁₁ formed of resin and having a positive refractive power and a second lens L₄₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₄₂ includes a negative meniscus lens L₄₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₄₂₁ is preferably formed of resin.

The third lens group G₄₃ includes a positive meniscus lens L₄₃₁ whose convex surface is directed toward the object side. Further, the lens L₄₃₁ is preferably formed of resin.

The object-side surface of the first lens L₄₁₁, the image-plane-IMG-side surface of the second lens L₄₁₂, both surfaces of the lens L₄₂₁, and both surfaces of the lens L₄₃₁ are aspherical.

Values concerning the imaging lens according to fourth embodiment are given below.

-   The focal length of the imaging lens (f)=4.81 -   The F number=2.82 -   The diameter of the effective image circle of the imaging lens     (2Y)=6.00 -   The focal length of the first lens group G₄₁ (f₁)=3.914 -   The focal length of the first lens L₄₁₁ of the first lens group G₄₁     (f₁₁)=2.664 -   The focal length of the second lens L₄₁₂ of the first lens group G₄₁     (f₁₂)=−6.197 -   The refractive index of d-line of the first lens L₄₁₁ of the first     lens group G₄₁ (n₁)=1.531 -   The refractive index of d-line of the second lens L₄₁₂ of the first     lens group G₄₁ (n₂)=1.586 -   (Values concerning conditional expression 1)

f ₁ /f=0.814

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.430

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.055

-   (Values concerning conditional expression 4)

OP/2Y=0.89

-   r₁=1.43197 (aspherical surface) -   d₁=0.685 nd₁=1.531 νd₁=56.0 -   r₂=−100 -   d₂=0.40 nd₂=1.586 νd₂=29.9 -   r₃=3.77016 (aspherical surface) -   d₃=0.783 -   r₄=−1.68016 (aspherical surface) -   d₄=0.527 nd₃=1.614 νd₃=26.0 -   r₅=−2.61490 (aspherical surface) -   d₅=0.439 -   r₆=3.38180 (aspherical surface) -   d₆=1.209 nd₄=1.525 νd₄=56.2 -   r₇=3.13425 (aspherical surface) -   d₇=0.35 -   r₈=∞ -   d₈=0.30 nd₅=1.518 νd₅=59.0 -   r₉=∞ -   d₉=0.629 -   r₁₀=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=−3.03926, -   A₃=3.770×10⁻³, A₄=2.110×10⁻¹, -   A₅=−5.215×10⁻¹, A₆=1.420, -   A₇=−2.031, A₈=1.496, -   A₉=−5.070×10⁻¹, A₁₀=−6.780×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (third surface) -   K=15.92033, -   A₃=6.720×10⁻², A₄=−2.229×10⁻¹, -   A₅=5.130×10⁻¹, A₆=−8.541×10⁻¹, -   A₇=8.759×10⁻¹, A₈=−4.090×10⁻¹, -   A₉=2.512×10⁻³, A₁₀=4.776×10⁻³ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fourth surface) -   K=−1.98759, -   A₃=−7.700×10⁻³, A₄=−2.905×10⁻¹, -   A₅=6.869×10⁻¹, A₆=−6.389×10⁻¹, -   A₇=4.829×10⁻², A₈=2.372×10⁻¹, -   A₉=−1.428×10⁻², A₁₀=−3.500×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=−0.73390, -   A₃=−1.167×10⁻¹, A₄=2.322×10⁻², -   A₅=−7.073×10⁻², A₆=1.177×10⁻¹, -   A₇=−4.971×10⁻², A₈=−3.715×10⁻², -   A₉=5.698×10⁻², A₁₀=−1.732×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=−29.74450, -   A₃=−2.831×10⁻², A₄=−9.452×10⁻², -   A₅=5.242×10⁻², A₆=8.713×10⁻³, -   A₇=−4.049×10⁻³, A₈=−3.037×10⁻³, -   A₉=1.716×10⁻⁴, A₁₀=3.107×10⁻⁴ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−26.75000, -   A₃=3.918×10⁻², A₄=−5.862×10⁻², -   A₅=−7.185×10⁻⁴, A₆=1.100×10⁻², -   A₇=−1.442×10⁻³, A₈=−9.478×10⁻⁴, -   A₉=1.189×10⁻⁴, A₁₀=1.190×10⁻⁵ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0

FIG. 11 is a spherical aberration diagram of the image lens according to the fourth embodiment. FIG. 12 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the fourth embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 13 is a cross-sectional view along the optical axis of an imaging lens according to a fifth embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₅₁, a second lens group G₅₂, and a third lens group G₅₃. Further, an aperture ST of a given diameter is provided in near an object-side surface of the first lens group G₅₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₅₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₅₁ includes sequentially from the object side, a first lens L₅₁₁ formed of resin and having a positive refractive power and a second lens L₅₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₅₂ includes a negative meniscus lens L₅₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₅₂₁ is preferably formed of resin.

The third lens group G₅₃ includes a positive meniscus lens L₅₃₁ whose convex surface is directed toward the object side. Further, the lens L₅₃₁ is preferably formed of resin.

The object-side surface of the first lens L₅₁₁, the image-plane-IMG-side surface of the second lens L₅₁₂, both surfaces of the lens L₅₂₁, and both surfaces of the lens L₅₃₁ are aspherical.

Values concerning the imaging lens according to the fifth embodiment are given below.

-   The focal length of the imaging lens (f)=5.54 -   The F number=2.98 -   The diameter of the effective image circle of the imaging lens     (2Y)=7.76 -   The focal length of the first lens group G₅₁ (f₁)=4.148 -   The focal length of the first lens L₅₁₁ of the first lens group G₅₁     (f₁₁)=2.468 -   The focal length of the second lens L₅₁₂ of the first lens group G51     (f₁₂)=−5.119 -   The refractive index of d-line of the first lens L₅₁₁ of the first     lens group G₅₁ (n₁)=1.525 -   The refractive index of d-line of the second lens L₅₁₂ Of the first     lens group G₅₁ (n₂)=1.586 -   (Values concerning conditional expression 1)

f ₁ /f=0.749

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.482

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.061

-   (Values concerning conditional expression 4)

OP/2Y=0.89

-   r₁=2.67472 (aspherical surface) -   d₁=1.726 nd₁=1.525 νd₁=56.2 -   r₂=−1.95241 -   d₂=0.50 nd₂=1.586 νd₂=29.9 -   r₃=−6.13108 (aspherical surface) -   d₃=0.680 -   r₄=−1.19695 (aspherical surface) -   d₄=0.500 nd₃=1.586 νd₃=29.9 -   r₅=−1.85871 (aspherical surface) -   d₅=0.358 -   r₆=2.94676 (aspherical surface) -   d₆=1.602 nd₄=1.525 νd₄=56.2 -   r₇=2.39554 (aspherical surface) -   d₇=0.49 -   r₈=∞ -   d₈=0.16 nd₅=1.517 νd₅=64.2 -   r₉=∞ -   d₉=0.884 -   r₁₀=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=3.14216, -   A₃=−1.2089×10⁻², A₄=2.7648×10⁻², -   A₅=−8.1647×10⁻², A₆=2.7650×10⁻², -   A₇=3.4848×10⁻², A₈=1.8828×10⁻², -   A₉=−4.0905×10⁻², A₁₀=2.5779×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (third surface) -   K=15.00753, -   A₃=3.7908×10⁻², A₄=−6.7878×10⁻², -   A₅=1.1743×10⁻², A₆=1.3739×10⁻², -   A₇=−5.7311×10⁻³, A₈=1.4851×10⁻², -   A₉=−6.7008×10⁻³, A₁₀=9.5792×10⁻³ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fourth surface) -   K=−0.35222, -   A₃=7.3512×10⁻², A₄=−3.3802×10⁻², -   A₅=−2.0897×10⁻³, A₆=8.0265×10⁻³, -   A₇=−1.9788×10⁻³, A₈=−1.2087×10⁻², -   A₉=−3.7764×10⁻³, A₁₀=1.7200×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=−0.63013, -   A₃=2.9468×10⁻², A₄=−4.1733×10⁻², -   A₅=−1.8359×10⁻², A₆=1.4500×10⁻², -   A₇=11.1265×10⁻², A₈=3.6633×10⁻³, -   A₉=5.3822×10⁻⁴, A₁₀=−1.5887×10⁻³ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=−6.17316, -   A₃=5.0574×10⁻², A₄=−1.5384×10⁻¹, -   A₅=3.8851×10⁻², A₆=−1.8549×10⁻², -   A₇=−8.4243×10⁻⁴, A₈=−3.0233×10⁻³, -   A₉=9.1872×10⁻⁴, A₁₀=3.9158×10⁻⁴ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−0.97556, -   A₃=9.7678×10⁻³, A₄=−6.5119×10⁻², -   A₅=3.1257×10⁻³, A₆=6.0270×10⁻³, -   A₇=11.0456×10⁻³, A₈=−5.0459×10⁻⁴, -   A₉=−2.2440×10⁻⁴, A₁₀=5.4202×10⁻⁵ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆₌₌₀

FIG. 14 is a spherical aberration diagram of the image lens according to the fifth embodiment. FIG. 15 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the fifth embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 16 is a cross-sectional view along the optical axis of an imaging lens according to a sixth embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₆₁, a second lens group G₆₂, and a third lens group G₆₃. Further, an aperture ST of a given diameter is provided near an object-side surface of the first lens group G₆₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₆₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₆₁ includes sequentially from the object side, a first lens L₆₁₁ formed of resin and having a positive refractive power and a second lens L₆₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₆₂ includes a negative meniscus lens L₆₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₆₂₁ is preferably formed of resin.

The third lens group G63 includes a positive meniscus lens L₆₃₁ whose convex surface is directed toward the object side. Further, the lens L₆₃₁ is preferably formed of resin.

The object-side surface of the first lens L₆₁₁, the image-plane-IMG-side surface of the second lens L₆₁₂, both surfaces of the lens L₆₂₁, and both surfaces of the lens L₆₃₁ are aspherical.

Values concerning the imaging lens according to the sixth embodiment are given below.

-   The focal length of the imaging lens (f)=5.82 -   The F number=3.03 -   The diameter of the effective image circle of the imaging lens     (2Y)=7.13 -   The focal length of the first lens group G₆₁ (f₁)=4.347 -   The focal length of the first lens L₆₁₁ of the first lens group G₆₁     (f₁₁)=2.674 -   The focal length of the second lens L₆₁₂ of the first lens group G₆₁     (f₁₂)=−5.353 -   The refractive index of d-line of the first lens L₆₁₁ of the first     lens group G₆₁ (n₁)=1.525 -   The refractive index of d-line of the second lens L₆₁₂ of the first     lens group G₆₁ (n₂)=1.586 -   (Values concerning conditional expression 1)

f ₁ /f=0.747

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.500

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.061

-   (Values concerning conditional expression 4)

OP/2Y=0.90

-   r₁=1.66632 (aspherical surface) -   d₁=0.848 nd₁=1.525 νd₁=56.2 -   r₂=−7 -   d₂=0.41 nd₂=1.586 νd₂=29.9 -   r₃=5.59044 (aspherical surface) -   d₃=00.641 -   r₄=−1.62924 (aspherical surface) -   d₄=0.585 nd₃=1.586 νd₃=29.9 -   r₅=−3.15569 (aspherical surface) -   d₅=0.577 -   r₆=2.72084 (aspherical surface) -   d₆=1.313 nd₄=1.525 νd₄=56.2 -   r₇=3.18876 (aspherical surface) -   d₇=0.50 -   r₈=∞ -   d₈=0.40 nd₅=1.518 νd₅=59.0 -   r₉=∞ -   d₉=1.127 -   r₁₀=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=−3.01609, -   A₃=1.0871×10⁻³, A₄=1.4032×10⁻¹, -   A₅=−2.7001×10⁻¹, A₆=5.9949×10⁻¹, -   A₇=−7.2423×10⁻¹, A₈=4.5980×10⁻¹, -   A₉=−1.2424×10⁻¹, A₁₀=5.6962×10⁻³ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (third surface) -   K=16.67601, -   A₃=3.4965×10⁻², A₄=−1.0709×10⁻¹, -   A₅=2.1976×10⁻¹, A₆=−3.4938×10⁻¹, -   A₇=3.5735×10⁻¹, A₈=−1.6788×10⁻¹, -   A₉=2.6200×10⁻³, A₁₀=7.2397×10⁻³ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fourth surface)

K=1.34207,

-   A₃=−1.0281×10⁻², A₄=−1.3368×10⁻¹, -   A₅=3.3636×10⁻¹, A₆=−3.1012×10⁻¹, -   A₇=6.3608×10⁻², A₈=1.3921×10⁻¹, -   A₉=−4.2727×10⁻², A₁₀=−1.571×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=1.95140, -   A₃=−6.7664×10⁻², A₄=−3.6942×10⁻², -   A₅=−1.5277×10⁻², A₆=7.9071×10⁻², -   A₇=−1.3201×10⁻², A₈=−1.6839×10⁻², -   A₉=1.1801×10⁻², A₁₀=−1.6893×10⁻⁴ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=−7.53571, -   A₃=−3.1177×10⁻², A₄=−9.1640×10⁻², -   A₅=2.4116×10⁻², A₆=2.0426×10⁻², -   A₇=−5.7047×10⁻³, A₈=−2.7220×10⁻³, -   A₉=1.4993×10⁻⁴, A₁₀=2.2020×10⁻⁴, -   A₁₁=5.1933×10⁻⁵, A₁₂=−2.2015×10⁻⁷ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−8.21118, -   A₃=−6.8201×10⁻³, A₄=−5.2624×10⁻², -   A₅=1.4082×10⁻², A₆=3.3509×10⁻³, -   A₇=−1.5835×10⁻³, A₈=−3.9331×10⁻⁴, -   A₉=1.5916×10⁻⁴, A₁₀=−1.9994×10⁻⁵, -   A₁₁=7.4056×10⁻⁶, A₁₂=−1.8077×10⁻⁶ -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0

FIG. 17 is a spherical aberration diagram of the image lens according to the sixth embodiment. FIG. 18 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the sixth embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 19 is a cross-sectional view along the optical axis of an imaging lens according to a seventh embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₇₁, a second lens group G₇₂, and a third lens group G₇₃. Further, an aperture ST of a given diameter is provided near an object-side surface of the first lens group G₇₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₇₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₇₁ includes sequentially from the object side, a first lens L₇₁₁ formed of resin and having a positive refractive power and a second lens L₇₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₇₂ includes a negative meniscus lens L₇₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₇₂₁ is preferably formed of resin.

The third lens group G₇₃ includes a positive meniscus lens L₇₃₁ whose convex surface is directed toward the object side. Further, the lens L₇₃₁ is preferably formed of resin.

The object-side surface of the first lens L₇₁₁, the image-plane-IMG-side surface of the second lens L₇₁₂, both surfaces of the lens L₇₂₁, and both surfaces of the lens L₇₃₁ are aspherical.

Values concerning the imaging lens according to the seventh embodiment are given below.

-   The focal length of the imaging lens (f)=5.55 -   The F number=2.93 -   The diameter of the effective image circle of the imaging lens     (2Y)=7.76 -   The focal length of the first lens group G₅₁ (f₁)=4.148 -   The focal length of the first lens L₅₁₁ of the first lens group G51     (f₁₁)=2.478 -   The focal length of the second lens L₅₁₂ of the first lens group G51     (f₁₂)=−5.552 -   The refractive index of d-line of the first lens L₅₁₁ of the first     lens group G₅₁ (n₁)=1.525 -   The refractive index of d-line of the second lens L₅₁₂ of the first     lens group G₅₁ (n₂)=1.586 -   (Values concerning conditional expression 1)

f ₁ /f=0.748

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.446

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.061

-   (Values concerning conditional expression 4)

OP/2Y=0.93

-   r₁=2.65490 (aspherical surface) -   d₁=1.597 nd₁=1.525 νd₁=56.2 -   r₂=−2.02053 -   d₂=0.81 nd₂=1.586 νd₂=29.9 -   r₃=−6.12879 (aspherical surface) -   d₃=0.624 -   r₄=−1.18289 (aspherical surface) -   d₄=0.728 nd₃=1.586 νd₃=29.9 -   r₅=−1.82113 (aspherical surface) -   d₅=0.243 -   r₆=2.9694 (aspherical surface) -   d₆=1.537 nd₄=1.525 νd₄=56.2 -   r₇=2.36034 (aspherical surface) -   d₇=0.49 -   r₈=∞ -   d₈=0.16 nd₅=1.517 νd₅=64.2 -   r₉=∞ -   d₉=1.001 -   r₁₀=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=3.14560, -   A₃=−1.1554×10⁻², A₄=2.7909×10⁻², -   A₅=−8.1322×10⁻², A₆=2.7960×10⁻², -   A₇=3.5069×10⁻², A₈=−1.8760×10⁻², -   A₉=−4.1040×10⁻², A₁₀=2.5394×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (third surface) -   K=15.37508, -   A₃=3.8243×10⁻², A₄=−6.8852×10⁻², -   A₅=1.2500×10⁻², A₆=1.3566×10⁻², -   A₇=−6.0729×10⁻³, A₈=−1.5126×10⁻², -   A₉=−6.8507×10⁻³, A₁₀=9.5490×10⁻³ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fourth surface) -   K=−0.33783, -   A₃=6.7024×10⁻², A₄=−3.7942×10⁻², -   A₅=−3.1040×10⁻³, A₆=8.3810×10⁻³, -   A₇=−2.2691×10⁻⁴, A₈=−1.190×10⁻², -   A₉=−3.3813×10⁻³, A₁₀=−1.7174×10⁻² -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=−0.56503, -   A₃=2.7997×10⁻², A₄=−4.2903×10⁻², -   A₅=−1.8395×10⁻², A₆=1.3989×10⁻², -   A₇=1.0886×10⁻², A₈=3.4923×10⁻³, -   A₉=5.1587×10⁻⁴, A₁₀=−1.5298×10⁻³ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=−5.82771, -   A₃=5.4742×10⁻², A₄=−1.5264×10⁻¹, -   A₅=3.9188×10⁻², A₆=1.8601×10⁻², -   A₇=−6.4017×10⁻⁴, A₈=−3.0013×10⁻³, -   A₉=−9.0033×10⁻⁴, A₁₀=4.6109×10⁻⁴ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−1.00965, -   A₃=1.0458×10⁻², A₄=−6.5312×10⁻², -   A₅=2.9784×10⁻³, A₆=6.0879×10⁻³, -   A₇=1.1105×10⁻³, A₈=−4.9924×10⁻⁴, -   A₉=−2.2353×10⁻⁴, A₁₀=5.4487×10⁻⁵ -   A₁₁=0, A₁₂=0, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0

FIG. 20 is a spherical aberration diagram of the image lens according to the seventh embodiment. FIG. 21 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the seventh embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 22 is a cross-sectional view along the optical axis of an imaging lens according to an eighth embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₈₁, a second lens group G₈₂, and a third lens group G₈₃. Further, an aperture ST of a given diameter is provided in near an object-side surface of the first lens group G₈₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₈₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₈₁ includes sequentially from the object side, a first lens L₈₁₁ formed of resin and having a positive refractive power and a second lens L₈₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₈₂ includes a negative meniscus lens L₈₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₈₂₁ is preferably formed of resin.

The third lens group G₈₃ includes a positive meniscus lens L₈₃₁ whose convex surface is directed toward the object side. Further, the lens L₈₃₁ is preferably formed of resin.

The object-side surface of the first lens L₈₁₁, the image-plane-IMG-side surface of the second lens L₈₁₂, both surfaces of the lens L₈₂₁, and both surfaces of the lens L₈₃₁ are aspherical.

Values concerning the imaging lens according to the eighth embodiment are given below.

-   The focal length of the imaging lens (f)=5.86 -   The F number=2.81 -   The diameter of the effective image circle of the imaging lens     (2Y)=6.00 -   The focal length of the first lens group G₈₁ (f₁)=4.107 -   The focal length of the first lens L₈₁₁ of the first lens group G₈₁     (f₁₁)=2.642 -   The focal length of the second lens L₈₁₂ of the first lens group G₈₁     (f₁₂)=−5.230 -   The refractive index of d-line of the first lens L₈₁₁ of the first     lens group G₈₁ (n₁)=1.531 -   The refractive index of d-line of the second lens L₈₁₂ of the first     lens group G₈₁ (n₂)=1.585 -   (Values concerning conditional expression 1)

f ₁ /f=0.701

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.505

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.054

-   (Values concerning conditional expression 4)

OP/2Y=1.05

-   r₁=1.52386 (aspherical surface) -   d₁=0.886 nd₁=1.531 νd₁=56.0 -   r₂=−14.19258 -   d₂=0.500 nd₂=1.585 νd₂=29.9 -   r₃=3.95553 (aspherical surface) -   d₃=0.150 -   r₄=∞ (diaphragm aperture) -   d₄=0.603 -   r₅=−1.52883 (aspherical surface) -   d₅=1.032 nd₃=1.585 νd₃=29.9 -   r₆=−3.54490 (aspherical surface) -   d₆=0.431 -   r₇=2.81042 (aspherical surface) -   d₇=0.688 nd₄=1.531 νd₄=56.0 -   r₈=4.75007 (aspherical surface) -   d₈=0.350 -   r₉=∞ -   d₉=0.300 nd₅=1.518 νd₅=59.0 -   r₁₀=∞ -   d₁₀=1.360 -   r₁₁=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=0.03011, -   A₃=−7.681×10⁻⁴, A₄=−1.451×10⁻², -   A₅=5.480×10⁻², A₆=−6.288×10⁻², -   A₇=−3.507×10⁻³, A₈=4.884×10⁻², -   A₉=−1.041×10⁻², A₁₀=−2.584×10⁻², -   A₁₁=1.717×10⁻², A₁₂=−3.166×10⁻³, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (third surface) -   K=−262.41070, -   A₃=7.066×10⁻², A₄=2.098×10⁻¹, -   A₅=−3.580×10⁻¹, A₆=2.568×10⁻¹, -   A₇=−1.781×10⁻¹, A₈=−1.174×10⁻¹, -   A₉=4.417×10⁻¹, A₁₀=1.513×10⁻¹, -   A₁₁=−8.188×10⁻¹, A₁₂=4.381×10⁻¹, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=−0.20458, -   A₃=1.337×10⁻¹, A₄=−1.109, -   A₅=3.526, A₆=−5.780, -   A₇=2.158, A₈=4.642, -   A₉=−2.161, A₁₀=−7.334, -   A₁₁=8.225, A₁₂=−2.568, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=0, -   A₃=−3.131×10⁻³, A₄=−1.152×10⁻¹, -   A₅=2.164×10⁻², A₆=5.931×10⁻², -   A₇=−2.705×10⁻², A₈=−3.450×10⁻², -   A₉=6.309×10⁻², A₁₀=−3.952×10⁻², -   A₁₁=1.001×10⁻², A₁₂=−3.290×10⁻⁴, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−5.66349, -   A₃=−1.143×10⁻², A₄=−1.070×10⁻¹, -   A₅=3.556×10⁻², A₆=−3.155×10⁻², -   A₇=2.765×10⁻², A₈=3.026×10⁻³, -   A₉=−5.272×10⁻³, A₁₀=−2.099×10⁻³, -   A₁₁=1.982×10⁻³, A₁₂=−3.464×10⁻⁴, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (eighth surface) -   K=0, -   A₃=1.309×10⁻², A₄=−6.080×10⁻², -   A₅=−4.342×10⁻², A₆=4.041×10⁻², -   A₇=−5.412×10⁻³, A₈=−4.385×10⁻³, -   A₉=1.446×10⁻³, A₁₀=8.783×10⁻⁴, -   A₁₁=−7.679×10⁻⁴, A₁₂=1.669×10⁻⁴, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0

FIG. 23 is a spherical aberration diagram of the image lens according to the eighth embodiment. FIG. 24 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the eighth embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 25 is a cross-sectional view along the optical axis of an imaging lens according to a ninth embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₉₁, a second lens group G₉₂, and a third lens group G₉₃. Further, an aperture ST of a given diameter is provided in near an object-side surface of the first lens group G₉₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₉₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₉₁ includes sequentially from the object side, a first lens L₉₁₁ formed of resin and having a positive refractive power and a second lens L₉₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₉₂ includes a negative meniscus lens L₉₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₉₂₁ is preferably formed of resin.

The third lens group G₉₃ includes a positive meniscus lens L₉₃₁ whose convex surface is directed toward the object side. Further, the lens L₉₃₁ is preferably formed of resin.

The object-side surface of the first lens L₉₁₁, the image-plane-IMG-side surface of the second lens L₉₁₂, both surfaces of the lens L₉₂₁, and both surfaces of the lens L₉₃₁ are aspherical.

Values concerning the imaging lens according to the ninth embodiment are given below.

-   The focal length of the imaging lens (f)=5.83 -   The F number=2.85 -   The diameter of the effective image circle of the imaging lens     (2Y)=6.00 -   The focal length of the first lens group G₉₁ (f₁)=4.096 -   The focal length of the first lens L₉₁₁ of the first lens group G₉₁     (f₁₁)=2.721 -   The focal length of the second lens L₉₁₂ of the first lens group G₉₁     (f₁₂)=−5.861 -   The refractive index of d-line of the first lens L₉₁₁ of the first     lens group G₉₁ (n₁)=1.531 -   The refractive index of d-line of the second lens L₉₁₂ of the first     lens group G₉₁ (n₂)=1.614 -   (Values concerning conditional expression 1)

f ₁ /f=0.703

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.464

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.083

-   (Values concerning conditional expression 4)

OP/2Y=1.04

-   r₁=1.59179 (aspherical surface) -   d₁=0.902 nd₁=1.531 νd₁=56.0 -   r₂=−12.61783 -   d₂=0.500 nd₂=1.614 νd₂=26.0 -   r₃=5.11334 (aspherical surface) -   d₃=0.150 -   r₄=∞ (diaphragm aperture) -   d₄=0.672 -   r₅=−1.38250 (aspherical surface) -   d₅=0.820 nd₃=1.585 νd₃=29.9 -   r₆=−3.53554 (aspherical surface) -   d₆=0.452 -   r₇=2.28927 (aspherical surface) -   d₇=0.713 nd₄=1.531 νd₄=56.0 -   r₈=4.30289 (aspherical surface) -   d₈=0.350 -   r₉=∞ -   d₉=0.300 nd₅=1.518 νd₅=59.0 -   r₁₀=∞ -   d₁₀=1.404 -   r₁₁=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=−0.38370, -   A₃=3.924×10⁻³, A₄=−1.678×10⁻², -   A₅=7.203×10⁻², A₆=−6.170×10⁻², -   A₇=−1.017×10⁻², A₈=4.598×10⁻², -   A₉=−8.564×10⁻³, A₁₀=−2.197×10⁻², -   A₁₁=1.924×10⁻², A₁₂=−6.001×10⁻³, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (third surface) -   K=−520.91900, -   A₃=−5.803×10⁻², A₄=2.017×10⁻¹, -   A₅=−4.002×10⁻¹, A₆=2.411×10⁻¹, -   A₇=−1.650×10⁻¹, A₈=−3.943×10⁻², -   A₉=4.816×10⁻¹, A₁₀=8.477×10⁻², -   A₁₁=−9.535×10⁻¹, A₁₂=5.218×10⁻¹, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=−0.29894, -   A₃=1.182×10⁻¹, A₄=−1.111, -   A₅=3.518, A₆=−5.817, -   A₇=2.154, A₈=4.737, -   A₉=−2.082, A₁₀=−7.431, -   A₁₁=7.955, A₁₂=−2.334, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=0, -   A₃=−1.581×10⁻², A₄=−1.386×10⁻¹, -   A₅=2.287×10⁻², A₆=7.495×10⁻², -   A₇=−2.241×10⁻², A₈=−3.733×10⁻², -   A₉=6.006×10⁻², A₁₀=−3.983×10⁻², -   A₁₁=1.229×10⁻², A₁₂=−9.645×10⁻⁴, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−4.88849, -   A₃=−1.284×10⁻², A₄=−1.053×10⁻¹, -   A₅=3.798×10⁻², A₆=2.990×10⁻², -   A₇=2.833×10⁻², A₈=3.006×10⁻³, -   A₉=−5.488×10⁻³, A₁₀=−2.247×10⁻³, -   A₁₁=1.945×10⁻³, A₁₂=−3.121×10⁻⁴, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0     (eighth surface) -   K=0, -   A₃=1.263×10⁻², A₄=−5.937×10⁻², -   A₅=−4.202×10⁻², A₆=4.038×10⁻², -   A₇=−5.795×10⁻³, A₈=−4.555×10⁻³, -   A₉=1.535×10⁻³, A₁₀=1.003×10⁻³, -   A₁₁=−7.272×10⁻⁴, A₁₂=1.272×10⁻⁴, -   A₁₃=0, A₁₄=0, -   A₁₅=0, A₁₆=0

FIG. 26 is a spherical aberration diagram of the image lens according to the ninth embodiment. FIG. 27 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the ninth embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 28 is a cross-sectional view along the optical axis of an imaging lens according to a tenth embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₁₀₁, a second lens group G₁₀₂, and a third lens group G₁₀₃. Further, an aperture ST of a given diameter is provided in near an object-side surface of the first lens group G₁₀₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₁₀₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₁₀₁ includes sequentially from the object side, a first lens L₁₀₁₁ formed of resin and having a positive refractive power and a second lens L₁₀₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₁₀₂ includes a negative meniscus lens L₁₀₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₁₀₂₁ is preferably formed of resin.

The third lens group G₁₀₃ includes a positive meniscus lens L₁₀₃₁ whose convex surface is directed toward the object side. Further, the lens L₁₀₃₁ is preferably formed of resin.

The object-side surface of the first lens L₁₀₁₁, the image-plane-IMG-side surface of the second lens L₁₀₁₂, both surfaces of the lens L₁₀₂₁, and both surfaces of the lens L₁₀₃₁ are aspherical.

Values concerning the imaging lens according to the tenth embodiment are given below.

-   The focal length of the imaging lens (f)=5.85 -   The F number=2.77 -   The diameter of the effective image circle of the imaging lens     (2Y)=6.00 -   The focal length of the first lens group G₁₀₁ (f₁)=4.052 -   The focal length of the first lens L₁₀₁₁ of the first lens group     G₁₀₁ (f₁₁)=2.619 -   The focal length of the second lens L₁₀₁₂ of the first lens group     G₈₁ (f₁₂)=−5.260 -   The refractive index of d-line of the first lens L₁₀₁₁ of the first     lens group G₁₀₁ (n₁)=1.525 -   The refractive index of d-line of the second lens L₁₀₁₂ of the first     lens group G₁₀₁ (n₂)=1.614 -   (Values concerning conditional expression 1)

f ₁ /f=0.693

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.498

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.090

-   (Values concerning conditional expression 4)

OP/2Y=1.02

-   r₁=1.50641 (aspherical surface) -   d₁=0.891 nd₁=1.525 νd₁=56.2 -   r₂=−12.47284 -   d₂=0.500 nd₂=1.614 νd₂=26.0 -   r₃=4.42756 (aspherical surface) -   d₃=0.115 -   r₄=∞ (diaphragm aperture) -   d₄=0.812 -   r₅=−1.45975 (aspherical surface) -   d₅=0.800 nd₃=1.585 νd₃=29.9 -   r₆=3.55180 (aspherical surface) -   d₆=0.326 -   r₇=4.13906 (aspherical surface) -   d₇=1.004 nd₄=1.525 νd₄=56.2 -   r₈=13.09039 (aspherical surface) -   d₈=0.350 -   r₉=∞ -   d₉=0.300 nd₅=1.518 νd₅=59.0 -   r₁₀=∞ -   d₁₀=1.017 -   r₁₁=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=0.03232, -   A₃=−1.366×10⁻², A₄=9.175×10⁻³, -   A₅=−3.269×10⁻³, A₆=−3.712×10⁻³, -   A₇=−2.665×10⁻⁴, A₈=−9.958×10⁻⁴, -   A₉=1.409×10⁻⁴, A₁₀=−3.944×10⁻⁴, -   A₁₁=−3.339×10⁻⁴, A₁₂=−2.466×10⁻⁴, -   A₁₃=−1.169×10⁻⁴, A₁₄=−5.159×10⁻⁵, -   A₁₅=0, A₁₆=0     (third surface) -   K=4.32446, -   A₃=−1.857×10−2, A₄=−4.372×10⁻³, -   A₅=2.865×10⁻², A₆=2.531×10⁻², -   A₇=4.069×10⁻³, A₈=−2.507×10⁻², -   A₉=−4.423×10⁻², A₁₀=−1.167×10⁻¹, -   A₁₁=−2.360×10⁻², A₁₂=8.326×10⁻², -   A₁₃=6.333×10⁻², A₁₄=1.093×10⁻¹, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=0.08789, -   A₃=−4.653×10⁻², A₄=1.952×10⁻³, -   A₅=5.207×10⁻², A₆=−1.423×10⁻¹, -   A₇=−4.992×10⁻², A₈=−3.308×10⁻², -   A₉=5.644×10⁻², A₁₀=9.454×10⁻², -   A₁₁=7.390×10⁻², A₁₂=2.442×10⁻², -   A₁₃=−8.387×10⁻², A₁₄=−1.935×10⁻¹, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=1.38948, -   A₃=−6.625×10⁻², A₄=−3.120×10⁻², -   A₅=5.154×10⁻³, A₆=−2.099×10⁻², -   A₇=5.391×10⁻³, A₈=7.214×10⁻³, -   A₉=1.780×10⁻³, A₁₀=1.782×10⁻³, -   A₁₁=−6.889×10⁻⁴, A₁₂=−6.510×10⁻⁴, -   A₁₃=5.390×10⁻⁴, A₁₄=4.584×10⁻⁶, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−87.06180, -   A₃=5.566×10⁻³, A₄=−3.329×10⁻², -   A₅=−5.018×10⁻³, A₆=−6.864×10⁻³, -   A₇=1.668×10⁻³, A₈=2.155×10⁻³, -   A₉=1.203×10⁻³, A₁₀=1.028×10⁻³, -   A₁₁=−4.414×10⁻⁴, A₁₂=−3.270×10⁻⁴, -   A₁₃=−1.650×10⁻⁴, A₁₄=1.142×10⁻⁴, -   A₁₅=0, A₁₆=0     (eighth surface) -   K=5.33682, -   A₃=−9.203×10⁻³, A₄=−1.216×10⁻², -   A₅=−5.377×10⁻³, A₆=−8.844×10⁻⁴, -   A₇=−1.390×10⁻⁴, A₈=−1.337×10⁻⁴, -   A₉=1.498×10⁻⁴, A₁₀=−1.670×10⁻⁵, -   A₁₁=2.596×10⁻⁵, A₁₂=1.394×10⁻⁵, -   A₁₃=−4.734×10⁻⁶, A₁₄=−3.371×10⁻⁶, -   A₁₅=0, A₁₆=0

FIG. 29 is a spherical aberration diagram of the image lens according to the tenth embodiment. FIG. 30 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the tenth embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

FIG. 31 is a cross-sectional view along the optical axis of an imaging lens according to an eleventh embodiment. The imaging lens includes sequentially from an object side which is not illustrated, a first lens group G₁₁₁, a second lens group G₁₁₂, and a third lens group G₁₁₃. Further, an aperture ST of a given diameter is provided in near an object-side surface of the first lens group G₁₁₁. A cover glass CG formed by a parallel plate is arranged between the third lens group G₁₁₃ and an image plane IMG. Further, an optical receiving surface of an imaging element such as a CCD or a CMOS is arranged on the image plane IMG.

The first lens group G₁₁₁ includes sequentially from the object side, a first lens L₁₁₁₁ formed of resin and having a positive refractive power and a second lens L₁₁₁₂ formed of resin and having a negative refractive power, collectively forming a cemented lens having a positive refractive power.

The second lens group G₁₁₂ includes a negative meniscus lens L₁₁₂₁ whose convex surface is directed toward the image plane IMG. Further, the lens L₁₁₂₁ is preferably formed of resin.

The third lens group G₁₁₃ includes a positive meniscus lens L₁₁₃₁ whose convex surface is directed toward the object side. Further, the lens L₁₁₃₁ is preferably formed of resin.

The object-side surface of the first lens L₁₁₁₁, the image-plane-IMG-side surface of the second lens L₁₁₁₂, both surfaces of the lens L₁₁₂₁, and both surfaces of the lens L₁₁₃₁ are aspherical.

Values concerning the imaging lens according to the eleventh embodiment are given below.

-   The focal length of the imaging lens (f)=5.92 -   The F number=2.84 -   The diameter of the effective image circle of the imaging lens     (2Y)=6.00 -   The focal length of the first lens group G₁₁₁ (f₁)=4.053 -   The focal length of the first lens L₁₁₁₁ of the first lens group     G₁₁₁ (f₁₁)=2.449 -   The focal length of the second lens L₁₁₁₂ of the first lens group     G₁₁₁ (f₁₂)=−4.504 -   The refractive index of d-line of the first lens L₁₁₁₁ of the first     lens group G₁₁₁ (n₁)=1.525 -   The refractive index of d-line of the second lens L₁₁₁₂ of the first     lens group G₁₁₁ (n₂)=1.585 -   (Values concerning conditional expression 1)

f ₁ /f=0.685

-   (Values concerning conditional expression 2)

|f ₁₁ /f ₁₂|=0.544

-   (Values concerning conditional expression 3)

n ₂ −n ₁=0.061

-   (Values concerning conditional expression 4)

OP/2Y=1.03

-   r₁=1.49735 (aspherical surface) -   d₁=0.834 nd₁=1.525 νd₁=56.2 -   r₂=−7.32267 -   d₂=0.500 nd₂=1.585 νd₂=29.9 -   r₈=4.22544 (aspherical surface) -   d₃=0.119 -   r₄=∞ (diaphragm aperture) -   d₄=0.817 -   r₅=−1.45112 (aspherical surface) -   d₅=0.808 nd₃=1.585 νd₃=29.9 -   r₆=−3.70243 (aspherical surface) -   d₆=0.322 -   r₇=3.96134 (aspherical surface) -   d₇=1.005 nd₄=1.525 νd₄=56.2 -   r₈=13.50798 (aspherical surface) -   d₈=0.350 -   r₉=∞ -   d₉=0.300 nd₅=1.518 νd₅=59.0 -   r₁₀=∞ -   d₁₀=1.112 -   r₁₁=∞ (image plane)     Constant of the cone (K) and Aspherical surface coefficient (A₃, A₄,     A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆)     (first surface) -   K=0.03987, -   A₃=−1.353×10⁻², A₄=8.776×10⁻³, -   A₅=−2.661×10⁻³, A₆=−3.527×10⁻³, -   A₇=−2.619×10⁻⁴, A₈=9.324×10⁻⁴, -   A₉=4.457×10⁻⁵, A₁₀=−4.966×10⁻⁴, -   A₁₁=−4.100×10⁻⁴, A₁₂=−2.826×10⁻⁴, -   A₁₃=−1.023×10⁻⁴, A₁₄=6.865×10⁻⁶, -   A₁₅=0, A₁₆=0     (third surface) -   K=3.80487, -   A₃=−1.857×10⁻², A₄=−4.372×10⁻³, -   A₅=2.865×10⁻², A₆=2.531×10⁻², -   A₇=4.069×10⁻³, A₈=−2.507×10⁻², -   A₉=−4.423×10⁻², A₁₀=−1.167×10⁻¹, -   A₁₁=−2.360×10⁻², A₁₂=8.326×10⁻², -   A₁₃=6.333×10⁻², A₁₄=1.093×10⁻¹, -   A₁₅=0, A₁₆=0     (fifth surface) -   K=0.02922, -   A₃=−4.653×10⁻², A₄=1.952×10⁻³, -   A₅=−5.207×10⁻², A₆=−1.423×10⁻¹, -   A₇=−4.992×10⁻², A₈=−3.308×10⁻², -   A₉=5.644×10⁻², A₁₀=9.454×10⁻², -   A₁₁=7.390×10⁻², A₁₂=2.442×10⁻², -   A₁₃=−8.387×10⁻², A₁₄=−1.935×10⁻¹, -   A₁₅=0, A₁₆=0     (sixth surface) -   K=1.22120, -   A₃=−6.625×10⁻², A₄=−3.120×10⁻², -   A₅=5.154×10⁻³, A₆=−2.099×10⁻², -   A₇=5.391×10⁻³, A₈=7.214×10⁻³, -   A₉=1.780×10⁻³, A₁₀=1.782×10⁻³, -   A₁₁=−6.889×10⁻⁴, A₁₂=−6.510×10⁻⁴, -   A₁₃=5.390×10⁻⁴, A₁₄=4.584×10⁻⁶, -   A₁₅=0, A₁₆=0     (seventh surface) -   K=−81.82737, -   A₃=6.786×10⁻³, A₄=−3.301×10⁻², -   A₅=−5.191×10⁻³, A₆=−6.895×10⁻³, -   A₇=1.588×10⁻³, A₈=2.108×10⁻³, -   A₉=1.199×10⁻³, A₁₀=1.025×10⁻³, -   A₁₁=−4.454×10⁻⁴, A₁₂=−3.274×10⁻⁴, -   A₁₃=−1.640×10⁻⁴, A₁₄=1.154×10⁻⁴, -   A₁₅=0, A₁₆=0     (eighth surface) -   K=2.12700, -   A₃=−1.094×10⁻², A₄=−1.213×10⁻², -   A₅=−5.147×10⁻³, A₆=−7.867×10⁻⁴, -   A₇=−1.224×10⁻⁴, A₈=−1.397×10⁻⁴, -   A₉=1.445×10⁻⁴, A₁₀=−1.892×10⁻⁵, -   A₁₁=2.527×10⁻⁵, A₁₂=1.377×10⁻⁵, -   A₁₃=−4.789×10⁻⁶, A₁₄=−3.417×10⁻⁶, -   A₁₅=0, A₁₆=0

FIG. 32 is a spherical aberration diagram of the image lens according to the eleventh embodiment. FIG. 33 is an astigmatism diagram in d-line (λ=587.56 nm) and a distortion diagram of the imaging lens according to the eleventh embodiment. In the astigmatism diagram, S is the sagittal image surface; M is the meridional image surface.

Further in the above numeric data, r₁, r₂ . . . respectively represent radii of curvature of the lens surfaces; d₁, d₂ . . . respectively represent the thicknesses of the lenses or surface intervals thereof; nd₁, nd₂ . . . respectively represent refractive indexes in d-line (λ=587.56 nm); vd₁, vd₂. . . respectively represent Abbe numbers in d-line (λ=587.56 nm) of lenses.

Further, each of the above aspherical surfaces can be expressed by the following equation, where with respect to the vertex as a point of reference, H is the height perpendicular to the optical axis, X(H) is the change in H along the direction of optical axis.

${X(H)} = {\frac{H^{2}/R}{1 + \sqrt{1 - {\left( {K + 1} \right){H^{2}/R^{2}}}}} + {A_{3}H^{3}} + {A_{4}H^{4}} + {A_{5}H^{5}} + {A_{6}H^{6}} + {A_{7}H^{7}} + {A_{8}H^{8}} + {A_{9}H^{9}} + {A_{10}H^{10}} + {A_{11}H^{11}} + {A_{12}H^{12}} + {A_{13}H^{13}} + {A_{14}H^{14}} + {A_{15}H^{15}} + {A_{16}H^{16}}}$

R represents paraxial radii of curvature, K represents constant of the cone, A₃, A₄, A₅, A₆, A₈, A₉, A₁₀, A₁₁, A₁₂, A₁₃, A₁₄, A₁₅, A₁₆ represent 3^(rd), 4^(th), 5^(th), 6^(th), 7^(th), 8^(th), 9^(th), 10^(th), 11^(th), 12^(th), 13^(th), 14^(th) 15^(th), 16^(th) aspherical coefficients, respectively.

As explained above, the imaging lens according to the present invention has the above characteristics and enables the provision of a small, low-cost, and light-weight imaging lens having a high optical performance satisfying the high pixel formation of an imaging element, even when lens formed of resin is included.

Further, by preferably using a lens having an aspherical surface, various aberrations can be corrected more effectively, while achieving a smaller and lighter optical system, and reducing production costs.

Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.

The present document incorporates by reference the entire contents of Japanese priority document, 2008-156614 filed in Japan on Jun. 16, 2008, and Japanese priority document, 2009-100022 filed in Japan on Apr. 16, 2009. 

1. An imaging lens comprising: a first lens group that includes sequentially from an object side, a first lens formed of resin and having a positive refractive power and a second lens formed of resin and having a negative refractive power, the first lens and the second lens collectively forming a cemented lens having a positive refractive power; a second lens group that includes a negative lens; a third lens group that includes a positive lens, wherein the first lens group, the second lens group, and the third lens groups are sequentially arranged from the object side.
 2. The imaging lens according to claim 1, wherein a condition: 0.5<f ₁ /f<1.0 is satisfied, where f₁ represents a focal length of the first lens group and f represents a focal length of the imaging lens.
 3. The imaging lens according to claim 1, wherein conditions: 0.3<|f₁₁ /f ₁₂|<1.0; and 0<n ₂ −n ₁ are satisfied, where f₁₁ represents a focal length of the first lens of the first lens group, f₁₂ represents a focal length of the second lens of the first lens group, n₁ represents a refractive index at d-line of the first lens of the first lens group, and n₂ represents a refractive index at the d-line of the second lens of the first lens group.
 4. The imaging lens according to claim 1, wherein a condition: OP/2Y<2.0 is satisfied, where OP represents an overall length of the imaging lens, and 2Y represents a diameter of an effective image circle of the imaging lens.
 5. The imaging lens according to claim 1, wherein at least one lens surface is aspherical.
 6. The imaging lens according to claim 1, wherein a lens formed of resin is used for the second lens group.
 7. The imaging lens according to claim 1, wherein a lens formed of resin is used for the third lens group. 